The contract encompasses two major activities: synthesis and repository-related activities. The latter includes deep freeze storage, analysis, purification and shipping of radiolabeled compounds. About 70% of the annual budget is utilized for synthesis and the remainder is required to cover expenses incurred to maintain the repository-related activities including the deep freeze storage facility (-70 degrees Celsius) radio-safety and radio-waste disposal. The estimated value of the stored compounds now number 115 exceeds $1,000,000. The compounds selected for syntheses involve both synthetics and natural products and cover a wide variety of chemical structures and complexity. The major focus will be on the synthesis of 3H-labeled compounds of high specific activity as well as 14C-labeled compounds. New radiolabeled syntheses are initiated upon program request derived from RAID program, the Drug Development Group (DDG), Operating Committee (OC), and Joint Development Committee (JDC) initiatives, and also from NIH RAID program. The radiolabeled compounds are used primarily to support preclinical pharmacology, toxicology, and mechanism of action studies. These studies are critical for successful drug development since they help the investigators define important properties, such as the in vivo fate of the parent compound. Furthermore, radiolabeled agents are used to identify metabolites, select the optimal route of drug administration, and monitor the biological disposition of compounds.